Maybe I'm going a bit off topic here; I like the revealed audits as they (to me anyway) pay more in stress relief in the long run.
Although it might be $5 gas, 2 gallons of gas or an inside purchase of $1 or $2 in reimbursement on top of the shop pay, I still feel like I'm ahead at the end of the day. I always come home with things I would never elsewise purchase along with a full tank of gas.
But, really, my gas is more than reimbursed for traveling to areas where there might be a good ethnic grocery (good bread, cheese, olives, etc), an orchard, maybe a wine shop that I know sells reasonably priced varieties or a nice drive in parts unknown.
When its warm, I can stop at a beach town and enjoy the sun for a few hours, do some writing, have a coffee or something refreshing in the town and be on my way.
The bonuses are great and often, they are showing up more and more. I really don't negotiate, I just watch the postings and have my own algorithm for determining their acceptability.